It appears the file is a Linux ext4 file system, we are going to mount it to view its content.

mount secretArchive.6303dd5dbddb15ca9c4307d0291f77f4 /mnt/tmp

The file system contains 1986 files, most of them are ASCII text from The Venona Story. One file, "secret1337" appears to be different from the others, it's a ZIP archive protected with a password. Unfortunately it's just a decoy.

Recovering deleted files

We are going to extract all deleted files from this Linux file system with extundelete.

The previous command will generate a bunch of new ASCII text files but also a hidden file named ".secret31337".After issuing a file command we know that this is a KGB Archiver file with compression level 3.

The last step is to download KGB Archiver and decompress the archive to get the flag.